To provide good thickness control, as well as good strip profile and flatness control, intermediate feedback signals have to be provided indicative of these parameters as they are measured between mill stands.
In a cold tandem mill, such measurements and feedback control are a common practice.
In hot strip mills, the installation of thickness and profile gages is difficult due to the action of loopers which are a part of the strip interstand tension control mechanism. In the state of the art, as represented, for example, by H. Harakei et al., Hot Strip Mill Gage Control Using Interstand Thickness Meter, Iron and Steel Engineer, August, 1992, pages 54-59, special correction for change in angularity of the strip in respect to an X-ray beam is provided. However, such correction cannot be perfect, so it increases an error of measurement, and also makes control more complicated.
The most appropriate position for an intermediate profile gage would be after stand F3 of a 6-stand mill and after stand F4 of a 7-stand mill. This is due to decreased value of allowable changes in relative crown at this point. Therefore, the desired crown-to-thickness ratio (relative strip crown) has to be obtained after those respective stands, as illustrated in FIGS. 1 and 2.